K252a Prevents Microglial Activation Induced by Anoxic Stimulation of Carotid Bodies in Rats.

Inducing carotid body anoxia through the administration of cyanide can result in oxygen deprivation. The lack of oxygen activates cellular responses in specific regions of the central nervous system, including the Nucleus Tractus Solitarius, hypothalamus, hippocampus, and amygdala, which are regulated by afferent pathways from chemosensitive receptors. These receptors are modulated by the brain-derived neurotrophic factor receptor TrkB. Oxygen deprivation can cause neuroinflammation in the brain regions that are activated by the afferent pathways from the chemosensitive carotid body. To investigate how microglia, a type of immune cell in the brain, respond to an anoxic environment resulting from the administration of NaCN, we studied the effects of blocking the TrkB receptor on this cell-type response. Male Wistar rats were anesthetized, and a dose of NaCN was injected into their carotid sinus to induce anoxia. Prior to the anoxic stimulus, the rats were given an intracerebroventricular (icv) infusion of either K252a, a TrkB receptor inhibitor, BDNF, or an artificial cerebrospinal fluid (aCSF). After the anoxic stimulus, the rats were perfused with paraformaldehyde, and their brains were processed for microglia immunohistochemistry. The results indicated that the anoxic stimulation caused an increase in the number of reactive microglial cells in the hypothalamic arcuate, basolateral amygdala, and dentate gyrus of the hippocampus. However, the infusion of the K252a TrkB receptor inhibitor prevented microglial activation in these regions.

Molecular tracking of insulin resistance and inflammation development on visceral adipose tissue.

Background: Visceral adipose tissue (VAT) is one of the most important sources of proinflammatory molecules in obese people and it conditions the appearance of insulin resistance and diabetes. Thus, understanding the synergies between adipocytes and VAT-resident immune cells is essential for the treatment of insulin resistance and diabetes. Methods: We collected information available on databases and specialized literature to construct regulatory networks of VAT resident cells, such as adipocytes, CD4+ T lymphocytes and macrophages. These networks were used to build stochastic models based on Markov chains to visualize phenotypic changes on VAT resident cells under several physiological contexts, including obesity and diabetes mellitus. Results: Stochastic models showed that in lean people, insulin produces inflammation in adipocytes as a homeostatic mechanism to downregulate glucose intake. However, when the VAT tolerance to inflammation is exceeded, adipocytes lose insulin sensitivity according to severity of the inflammatory condition. Molecularly, insulin resistance is initiated by inflammatory pathways and sustained by intracellular ceramide signaling. Furthermore, our data show that insulin resistance potentiates the effector response of immune cells, which suggests its role in the mechanism of nutrient redirection. Finally, our models show that insulin resistance cannot be inhibited by anti-inflammatory therapies alone. Conclusion: Insulin resistance controls adipocyte glucose intake under homeostatic conditions. However, metabolic alterations such as obesity, enhances insulin resistance in adipocytes, redirecting nutrients to immune cells, permanently sustaining local inflammation in the VAT.

Leptin in the Commissural Nucleus of the Tractus Solitarius (cNTS) and Anoxic Stimulus in the Carotid Body Chemoreceptors Increases cNTS Leptin Signaling Receptor and Brain Glucose Retention in Rats.

Background and Objectives: The commissural nucleus of the tractus solitarius (cNTS) not only responds to glucose levels directly, but also receives afferent signals from the liver, and from the carotid chemoreceptors (CChR). In addition, leptin, through its receptors in the cNTS, regulates food intake, body weight, blood glucose levels, and brain glucose retention (BGR). These leptin effects on cNTS are thought to be mediated through the sympathetic-adrenal system. How these different sources of information converging in the NTS regulate blood glucose levels and brain glucose retention remains largely unknown. The goal of the present study was to determine whether the local administration of leptin in cNTS alone, or after local anoxic stimulation using sodium cyanide (NaCN) in the carotid sinus, modifies the expression of leptin Ob-Rb and of c-Fos mRNA. We also investigated how leptin, alone, or in combination with carotid sinus stimulation, affected brain glucose retention. Materials and Methods: The experiments were carried out in anesthetized male Wistar rats artificially ventilated to maintain homeostatic values for pO2, pCO2, and pH. We had four groups: (a) experimental 1, leptin infusion in cNTS and NaCN in the isolated carotid sinus (ICS; n = 10); (b) experimental 2, leptin infusion in cNTS and saline in the ICS (n = 10); (c) control 1, artificial cerebrospinal fluid (aCSF) in cNTS and NaCN in the ICS (n = 10); (d) control 2, aCSF in cNTS and saline in the ICS (n = 10). Results: Leptin in cNTS, preceded by NaCN in the ICS increased BGR and leptin Ob-Rb mRNA receptor expression, with no significant increases in c-Fos mRNA in the NTSc. Conclusions: Leptin in the cNTS enhances brain glucose retention induced by an anoxic stimulus in the carotid chemoreceptors, through an increase in Ob-Rb receptors, without persistent changes in neuronal activation.

Moderate and high intensity chronic exercise reduces plasma tumor necrosis factor alpha and increases the Langerhans islet area in healthy rats.

OBJECTIVE: This study aimed to examine the effects of moderate (MIT) and high-intensity training (HIT) chronic exercise on plasma tumor necrosis factor alpha (TNF-α) level and its impact on Langerhans islet morphology in healthy rats. METHODS: Two-month old normal male Wistar rats were divided into three groups: control (C, n=6), MIT (n=6), and HIT (n=4). The training protocol consisted in 24 sessions of running on a treadmill at 60-80% maximal oxygen consumption (VO2max) for MIT, and >80% VO2max for HIT. TNF-α and insulin were measured with ELISA tests. Duodenal pancreas was dissected to analyze the Langerhans islets by immunohistochemistry, a correlation analysis was performed with the nuclei/total islet area. Results: HIT and MIT rats showed lower TNF-α plasma levels than controls. Plasma insulin level decreased significantly in HIT compared with C and MIT. In addition, the islet area and nuclei density per islet were higher in the exercise groups compared with C. However, none of the groups showed PD1 immunoreactivity. CONCLUSIONS: Under healthy conditions, the chronic exercise reduced plasmatic TNF-α level, and in the same sense, increased the size of the Langerhans islets, depending to the exercise intensity.

Nitric oxide in the nucleus of the tractus solitarius is involved in hypoglycemic conditioned response.

The repeated injection of insulin (unconditioned stimulus, UCS) immediately followed by exposure to sensory stimulation (e.g. sound or odor; conditioned stimulus, CS) results in a learned conditioned reflex in which the exposure to the CS alone lowers blood glucose. The brain regions participating in this hypoglycemic Pavlovian response remain unknown. Here we investigate if nitric oxide (NO) in the nucleus tractus solitarius (NTS), a nucleus known to be involved in glucose homeostasis, participates in this hypoglycemic reflex. Insulin injections (UCS) were paired with exposure to menthol odor (CS). After 8-10 reinforcements (4-5days training), rats acquire the learned hypoglycemic response. An increase in c-Fos expression was observed in the NTS, the ventrolateral hypothalamic nucleus (VLH) and other brain regions of conditioned rats. Microinjections of 3-(5'-hydroxymethyl-2'furyl)-1-benzyl indazole (YC-1) a stimulator of soluble guanylate cyclase (sGC) into NTS before the UCS accelerated the acquisition of the learned hypoglycemic response; 5-6 reinforcement produced pronounced glucose drop when exposed to the CS. In contrast, an inhibitor of NO synthase (NOS) Nω-Nitro-l-arginine methyl ester (L-NAME) in the NTS prolonged the required training period (11-15 reinforcements) to obtain the hypoglycemic reflex, and reduced the glycemic response. The number of c-Fos expressing cells in the NTS and VLH in rats receiving YC-1was significantly higher than that observed in rats receiving L-NAME. These findings suggest that NO-cGMP-PKG signaling in the NTS can modify the acquisition of conditioned hypoglycemia, and suggests that this nucleus directly participates in this reflex.

Effect of moderate and high intensity chronic exercise on the pancreatic islet morphometry in healthy rats: BDNF receptor participation.

The function and morphology of ß-cells is largely dependent on insulin demand. As ß-cells cover a bigger cell proportion in pancreas islets, changes of insulin producer cells affect the whole pancreatic islet morphology. Growth factors as the neurotrophins regulate the pancreas physiology, besides; physical exercise increases insulin sensitivity, and further modifies brain derived neurotrophic factor (BDNF) concentration in plasma. The aim of this study was to investigate the effects of chronic exercise (running in a treadmill for 8 weeks) intensity on pancreatic islet morphometry in healthy state. The BDNF receptor effect on the pancreatic islet morphometry was also evaluated. Adult male Wistar rats were divided in 6 groups: Control (C); moderate intensity training (MIT); high intensity training (HIT) did not treat with BDNF receptor inhibitor (K252a), and C, MIT and HIT treated with K252a. The results shown that chronic exercise induces ß-cells hypertrophy without BDNF receptor participation. On the other hand, the moderate exercise increases the number of ß cells per islet; the last effect does not require TrkB participation. In sedentary conditions, the K252a treatment reduced the ß-cell density. Exercise intensity has differential effects on pancreas islet morphometry in healthy model; furthermore, BDNF receptor plays a role to maintain the amount of ß-cells in sedentary state.

Nitric oxide in the commissural nucleus tractus solitarii regulates carotid chemoreception hyperglycemic reflex and c-Fos expression.

Carotid body chemoreceptors function as glucose sensors and contribute to glucose homeostasis. The nucleus tractus solitarii (NTS) is the first central nervous system (CNS) nuclei for processing of information arising in the carotid body. Here, we microinjected a nitric oxide (NO) donor sodium nitroprusside (SNP), an NO-independent activator of the soluble guanylyl cyclase (sGC) (YC1) or an NO-synthase (NOS) inhibitor Nω-nitro-l-arginine methyl ester (L-NAME) into the commissural NTS (cNTS) before carotid chemoreceptor anoxic stimulation and measured arterial glucose and the expression of Fos-like immunoreactivity (Fos-ir). Male Wistar rats (250-300 g) were anesthetized, and the carotid sinus was vascularly isolated. Either artificial cerebrospinal fluid (aCSF), SNP, YC1 or L-NAME were stereotaxically injected into the cNTS. The SNP and YC1 infused into the cNTS before carotid chemoreceptor stimulation (SNP-2 and YC1-2 groups) similarly increased arterial glucose compared to the aCSF-2 group. By contrast, infusion of L-NAME into the cNTS before carotid chemoreceptor stimulation (L-NAME-2 group) decreased arterial glucose concentration. The number of cNTS Fos-ir neurons, determined in all the groups studied except for YC1 groups, significantly increased in SNP-2 rat when compared to the aCSF-2 or SNP-2 groups. Our findings demonstrate that NO signaling, and the correlative activation of groups of cNTS neurons, plays key roles in the hyperglycemic reflex initiated by carotid chemoreceptor stimulation.

Concomitant effects of nitric oxide and carotid chemoreceptor stimulation on brain glucose in normoglycemic and hyperglycemic rats.

BACKGROUND AND AIMS: Carotid body (CB) sinus perfusion with different glucose concentrations modifies arterial glucose concentration and brain glucose retention, thereby changing the brain's threshold to hypoxia. Because nitric oxide (NO) modulates hypoxic chemoreception, we investigated the relationship between NO- and CB-receptor pathways on arterial glucose and brain arteriovenous (a-v) glucose difference after hypoxic stimulation under hyperglycemic conditions. METHODS: Normoglycemic and streptozotocin (STZ, 50 mg/kg i.p.)-induced hyperglycemic Sprague Dawley rats were infused with the NO donor, sodium nitroprusside (SNP), or the NOS inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME) into the circulatory isolated carotid sinus after (30 sec) local anoxic CB chemoreceptor stimulation with sodium cyanide (NaCN). RESULTS: L-NAME abolished the hyperglycemia and the increase in brain a-v glucose concentration difference induced by CB chemoreceptor stimulation in normoglycemic rats, whereas the same treatment in hyperglycemic rats did not change the glucose variables studied. However, SNP infused under the same conditions induced a bigger rise in arterial glucose and brain a-v glucose concentration difference only in normoglycemic rats, when compared with the results obtained in sham-2-control rats. CB stimulation plus SNP treatment also resulted in an increase in nitrite levels in cephalic venous blood in normoglycemic, but not in hyperglycemic, rats. CONCLUSIONS: We showed a clear concomitant effect of SNP infusion into local CB circulation and anoxic cyanide stimulation, enhancing hyperglycemia and brain a-v glucose concentration difference. Importantly, at high glucose levels, nitrergic drugs did not modify glucose variables when compared with the corresponding sham controls.